Since after birth the supply of nutrients to the body is maintained by intestinal absortion, derangements of intestinal absorption could adversely affect proper growth and development of the infant and child. To be able to recognize deranged intestinal function as a possible cause for abnormal growth and development, it is essential that we known the normal. However, information regarding normal intestinal function (especially its absorptive properties) is lacking and scanty for infants and children. The purpose of this research is to study by in vivo perfusion methods, the development of absorptive functions of the small intestine under normal conditions in growing animals and humans. The normal data will serve as baseline for assessing abnormal intestinal function. More basic and extensive studies will be done in an animal model. The developmental characteristics of absorption of glucose, galactose, glycine, valine and lysine and calcium and magnesium will be studied in situ, under steady state conditions by in vivo perfusion techniques in rats aged 7-8, 14-15, 21-23, 28-31 and 70-73 days. Absorption in malnourished and diabetic pups will be compared to that in normal pups. Small intestinal absorption of hexoses (glucose and galactose) and minerals (calcium and magnesium) will be measured in normal infants and in those suspected of having defects of intestinal absorption. Th triple lumen tube method for study of intestinal absorption to be used in infants and children will be evaluated in rats. A marker for estimating the mucosal surface area of the perfused segment will be tested in this model. This will allow expressing absorption rates on the basis of mucosal surface area rather than length of the segment perfused.